Cathodic protection of printing apparatus



Jan. 19, 1965 E; B. OWREN I 3,166,487

CATHODIC PROTECTION OF PRINTING APPARATUS Filed Feb. 14, 1962 United States Patent M 3,166,487 CATHQDEC PROTESTIGN 0F PRHQTIN t APPARATUS Erling B. Owl-en, FosterCenter, Pi, assignor to Cranston Print Works Company, Cranston, iii, a corporation of Rhode Island I ....Filed Feb..14,:l962, Ser..No. 173,17 -;1.Claim.-:(Cl. 204e1%) This invention relates to equipment for printing repetitive designs. on elongated webs of fabricated material such as textile fabric, paper and the like; More particularly the invention isdirected toward improvements in such equipment and its manner ofuse designed to control and eliminate undesirable pitting of metallic doctor blades when used' with printing: rolls in certain of such equipment. H

' In roller printing machines, for example of the type used in printing on textile fabric webs, customary equipment includes-i a reservoir called a color box, containing a supply of the printing-paste or ink which is spread on the engraved surface of a print roll, a steel or other metallic doctor blade being applied-against the roll to smooth the paste into the engraved depressions on the roll and to remove unwanted-or excess paste from the unengraved outer'surface portions, and a rotating printing cylinder orother traversing means carrying'the fabric web past the doctored surface of the print roll, with enough pressure between print roll and printing cylinder to transfer or print'thepaste from the engraved depressions to. the moving fabric: If the doctor blade' does not remove all the unwanted excess paste from the surface of the engraved print roll, streaks will be left on the roll which will appear-"as undesirable stripes on the fabric when the printing cylinder applies the fabric against the print. roll; Any cracks, nicks,'or other unevenness in the edge of the doctor blade must therefore be avoided or unsalable streaked printed fabric will be produced. Unfortunately it has been common that, after a relatively short period of use, the edge of a doc-tor blade in roller printing machines of the type described becomes pitted or etched-to-such-adegree that the machine must be stopped, the doctor-blade removed and replaced or redressed'as by-refiling and" restoning before the machine can again produce satisfactory printing. The principal object-- of thepresent invention therefore is to provide means and techniques to control and eliminate the pitting of-me-tallic doctor blades for printing rolls in printing machines ofthe class-described. As a result of this invention webs of fabricated materials may be satisfactorily printed at less cost, more rapidly and with higher quality than previously.

Other objects, advantages and further details of that which is believed to be novel and included in this invention will be clear from the following description and claims, taken with the accompanying drawing in which is illustrated by way of example one successful embodiment of the invention applied to a roller printing machine for textile fabrics.

In the drawing:

FIG. 1 is a vertical section through the active printing parts of a roller printing machine showing somewhat diagrammatically one form of the present invention applied thereto, and

FIG. 2 is a top plan view of part of the mechanism shown in FIG. 1.

In the exemplary printing machine will be found the usual reservoir or color box 6 containing the printing paste or ink 7. The color box is made of metal or has metal parts, usually copper. A rotatable fiber or nylon brush roll 8 dips into the reservoir of paste and upon rotation carries the paste and spreads it against the 3,166,487. Patented Jan. 119, 1965 outer surface of a rotatable print roll 9 having a repetitive 'designengraved in its outer copper or other metal surface; It is from this roll that the paste is printed or applied against the fabric F, carried by the traversing printing machine cylinder 11 past the print roll, sufficient pressure beingexerted between the print roll and the printing cylinder to transfer or so the engraved design on thefabric.

Obviously, all of the printing paste initially spread by the brush rollon the surface of the print roll is not wanted, but "only those portions of the paste Within the depressions of the engraved surface are desired to be transferred: Therefore, it is customary, to apply the edge of a steel or other metal doctor blade 12 against the surface of the print roll in advance of the spot Where the roll reaches the fabric, so that unwanted printing paste or ink is removed from the roll and will not appear as part ofthe "printed design. The doctor blade 12 is firmly but 'adjustably secured as by a mounting bar 13 on a suitable portion of the frame of the printing machine so that the engagement of the edge of the blade with the surface of-the print roll may be carefully maintained and adjusted. A clamping bar 14, held in place as by-a series'of bolts 15 and cooperating nuts 16 in known fashion, assists in securing the blade to the mounting bar in proper'position and condition to function.

Equipment so far described is conventional and known, and the operation of this equipment for relatively short periods of time" will show pitting or etching of the edge of the doctor blade as earlier discussed. The present invention is'designed to prevent this pitting or etching of'the edge of the doctor blade and is based upon the discovery that the pitting is largely due to the electrolytic action occurring in' a voltaic cell or couple which includes the steel doctor blade as the anode; the printing paste or ink as the electrolyte (being a solution of dye, thickeners and color developing chemicals), and the usual copper bearingcolor box (and various other metal parts of the equipment in contact'with the paste) as the cathode of the cell. Because an electrolytic cell is reversible and controllable, at first it was tried to use the stationary color'box as one electrode element, the fixed blade itself as the other electrode element and apply a direct current of sufficient strength to'reverse the cell, thereby making the doctor blade the cathode and the colorboxthe anode between which the printing paste electrolyte would be active. However, upon experiment, this arrangement proved to be impractical because when the reversingcurrent was applied to the color box the pitting or etching action continued on the doctor blade substantially as before. Further analysis indicated that perhaps the desired result failed of achievement because the color box is grounded to the printing machine proper, so that the small reversing current which was expected to suflice was groundedout and did not bring the desired reversal of the cell.

It was then determined that if the anode of the cell was isolated from the color box by using a separate electrode element in the color box electrically in sulated therefrom but in contact with the paste electrolyte, the protective system would function properly. Direct current of sufiicient strength (about one and one half volts at one fifth of an ampere) was applied to reverse the cell. The drawings illustrate an arrangement which was eminently satisfactory and, although the corrosive etching or pitting action normally noted was present, it was transferred to the interposed anodic electrode and appeared to be less than the normal pitting or etching which might be expected for a complete cell reversal.

The successful equipment shown in the drawing includes an aluminum electrode 17 secured to the color box as by an insulating clamp or support 18, the electrode extending into the printing paste or ink 7, near the bottom and across the width of the color box. In order to prevent accidental contact of this electrode with the color box, additional spacing insulators 19 are provided, which surround the electrode 17 where it extends close to the surfaces of the color box.

This electrode is connected as by a suitable wire and terminal 21 to the positive side of a direct current source of electromotive force 22 which may be a battery or other suitable instrumentality furnishing the reversal current above described.

The opposite or negative side of this direct current source is electrically connected in any suitable fashion, as by an insulated wire 23, to the doc-tor blade 12. This connection may be made easily by using one or more of the nuts 16 which hold the clamping bar 14 to the mounting bar 13 for the doctor blade. Proper current distribution along the blade may be obtained by added connections, if needed.

With the proper direct current imposed in the direction noted between the electrode 17 and the doctor blade 12, the cell was found to be reversed, so that the electrode 17 now became the anode, and the doctor blade, the cathode. The printing machine was run for considerable periods of time without any pitting of the doctor blade, and therefore the fabric could be printed without interruption for long periods of time, no streaked printing being produced. A sharper and better print quality is also an expected bonus because the negative charge imposed on the blade is opposite to the natural positive static charge in the fabric. This should result in more rapid and complete release of color from the engraving to the fabric under less critical conditions of set pressure. The cost of electrical energy consumed is more than otfset by the savings because of uninterrupted printing and fewer dressings of the blade.

Improvements to the arrangement might be made, for example by building the electrode 17 as a disc inserted flush into an insulated recess in the side or bottom walls of the color box, and by providing this electrode with a platinum plating or other corrosion-resistant surface in contact with the printing paste. Other metals than aluminum might also be used for this interposed electrode, used as an anode. Theoretically, the color box itself, if properly insulated electrically from ground and from all the other parts of the machine, might be used as the reversing electrode. Possible added difiiculties, such as anodic pitting of the color box, might have to be overcome in such an arrangement.

A further improvement or variation might include the use of a suitable 110 volt A.C.-D.C. rectifier at each print machine to provide the reversing voltage required. In such case a voltmeter or ammeter built into the rectifier could show the efliciency of the cell reversal and indicate proper alterations in the applied direct current to correct changes of conditions during operation of the machines.

As will be evident from the foregoing description, certain aspects of this invention are not limited to the particular details set forth as an example, and it is contemplated that various and other modifications and applications of the invention will occur to those skilled in the art. It is therefore intended that the appended claims shall cover such modifications and applications as do not depart from the true spirit and scope of the invention.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

In a rotary printing machine for fabrics which includes a color box constituting a reservoir containing printing paste, a rotatable print roll having a cylindrical outer copper printing surface, a rotatable brush roll in said color box for supplying printing paste from said reservoir and spreading it on the said surface of said print roll as it rotates, a steel doctor blade with an edge positioned against said cylindrical print roll surface to remove excess paste therefrom as it rotates, and a printing cylinder traversing and pressing a fabric web against said print roll printing surface following spreading of paste thereon by said brush roll and after removal of excess paste therefrom by the edge of said doctor blade, that improvement comprising a metal electrode insulatedly supported by said color box in contact with the paste contained therein, a source of direct current having a positive and a negative terminal, a conductor electrically connecting the positive terminal of said direct current source to said electrode and a conductor electrically connecting the negative terminal of said source to said doctor blade, whereby said blade is the cathode, said paste is the electrolyte and said electrode is the anode, and electrolytic corrosion and pitting of said blade edge is thereby prevented.

References Cited in the file of this patent UNITED STATES PATENTS 1,677,655 Reed et al. July 17, 1928 1,895,125 Durham Jan. 24, 1933 2,404,689 Carlsen et a1. July 23, 1946 2,916,429 Vossuack et a1. Dec. 8, 1959 2,996,445 Eisenberg et al Aug 15, 1961 3,017,340 Williams Jan. 16, 1962 3,025,790 Larsen Mar. 20, 1962 3,108,055 Grant Oct. 22, 1963 

